Gain measurement and monitoring for wireless communication systems

ABSTRACT

A system and method of monitoring a signal repeating device in a wireless communication system is provided. An operational noise measurement is obtained by measuring a noise value outside of a bandwidth of a first element, but within a bandwidth of a second, subsequent element in a signal path of the device. The operational noise measurement is alternatively obtained by tuning an input band of the device to shift the input band partially or completely outside of a bandwidth of a first element to create an open band or by suppressing an input of an antenna and measuring noise within the open bandwidth of the device. A stored parameter is retrieved and compared to the measured operational noise. Alternatively, a leakage signal of the device may be received at a signal receiver and compared to a reference. The reference is a function of elements of the device in a leakage path of the leakage signal.

RELATED APPLICATIONS

This application is a Continuation application of and claims the benefitof U.S. application Ser. No. 12/706,001, filed Feb. 16, 2010, entitled“GAIN MEASUREMENT AND MONITORING FOR WIRELESS COMMUNICATION SYSTEMS”,which application is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

The present invention is directed to wireless transceiver systems foruse in wireless communication systems, and specifically is directed togain monitoring in the wireless transceiver systems.

Contemporary cellular phone systems and broadband wireless metropolitannetworks are generally divided into a number of cells distributed in apattern to preclude co-channel interferences and provide coverage ofmobile and fixed subscriber units operating within the service area ofthe system. Each cell generally includes a base station that employsradio frequency (RF) transceiver equipment, antennas, and wire linecommunication equipment. In addition, some cells also include repeaters,distributed antenna systems (DAS), and/or remote radio heads in order toextend the coverage of the base station over longer distances,throughout buildings or tunnels, around obstacles, etc. These coverageextension elements, hereafter generically referred to as “repeaters”,serve to filter, amplify, and re-radiate signals in both directions,from the base station to subscriber units (the “downlink” direction),and from subscriber units back to the base station (the “uplink”direction).

A repeater is normally configured to provide either a fixed amount ofoutput power or a fixed amount of gain in each direction. Maintainingthe desired operating levels is critical to achieving optimal networkcoverage and performance. Simply measuring the output power of therepeater at any given time is inadequate to guarantee proper operation,as the input signal levels may vary over time.

Therefore there is a need in the art for an inexpensive system able tomonitor the total system gain and overall performance of a repeater, andto provide an indication if its performance falls outside pre-determinedlimits.

SUMMARY OF THE INVENTION

Embodiments consistent with the invention provide a method of monitoringat least one element of a wireless communication system. An operationalnoise measurement may be obtained by measuring a noise value outside ofa bandwidth of a first device, but within a bandwidth of a second,subsequent device. A stored parameter may be retrieved and the measuredoperational noise measurement may be compared to the retrievedparameter.

In other embodiments an input band of the element of the wirelesscommunication system may be tuned to shift the input band partially orcompletely outside of a bandwidth of a first device to create an openband. An operational noise level may be measured in the open band. Astored parameter is retrieved and may be compared to the measuredoperational noise level.

In still other embodiments, an operational noise level by may beobtained by suppressing an input of the antenna and measuring noisewithin a bandwidth of the element of the wireless communication network.A stored parameter is retrieved and compared to the measured operationalnoise level.

Some embodiments receive a leakage signal of the element of the wirelesscommunications system at a signal receiver. The received leakage signalmay then be compared to a reference. The reference may be a function ofcomponents of the wireless communication system in a leakage path of theleakage signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIGS. 1A and 1B contain a block diagram of an exemplary repeaterconsistent with embodiments of the invention.

FIG. 2 is a graph illustrating unused segments of an input band.

FIG. 3 is a graph illustrating available segments of a filter bandaround an input band.

FIG. 4 is a graph illustrating frequency shifting an input band tocreate an unused segment.

FIGS. 5A and 5B contain an alternate embodiment of the block diagram ofthe repeater in FIGS. 1A and 1B.

FIG. 6 contains an embodiment of a repeater indicating characterizedleakage paths.

FIG. 7 contains an embodiment of a repeater indicating characterizedleakage paths.

FIG. 8 contains an embodiment of a repeater indicating characterizedleakage paths.

FIGS. 9A and 9B are flowcharts for detecting front-end failures.

FIGS. 10A and 10B are flowcharts for detecting back-end failures.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the sequence of operations as disclosedherein, including, for example, specific dimensions, orientations,locations, and shapes of various illustrated components, will bedetermined in part by the particular intended application and useenvironment. Certain features of the illustrated embodiments have beenenlarged or distorted relative to others to facilitate visualization andclear understanding. In particular, thin features may be thickened, forexample, for clarity or illustration. Also, where appropriate, similarreference numbers have been used to indicate like parts.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are directed to an apparatus andmethod of measuring or monitoring gain in a wireless communicationsystem. Measurements of gain may be used for additional diagnostics,such as fault detection. For example, service providers are interestedin knowing whether an amplifier in the communication system has blown orwhether another component has failed, such that the communication systemis not operating properly, in order to quickly service or replace therepeater or component. Some contemporary communication systems use powerdetectors to monitor or measure output power; however, such solutionscannot measure total system gain or identify fault conditions in arepeater because the input signal level is not known. A second detectorcould be placed at the repeater input, but this solution would beexpensive due to the additional hardware and high dynamic rangerequired. Instead, the various embodiments of the present inventionoffer lower cost solutions for total system gain measurement and faultdetection. The methodology of the embodiments of the invention disclosedherein is illustrated in the form of a repeater; however, themethodology is generic enough to measure gain in many related types ofwireless communication system elements, such as Distributed AntennaSystems (DAS) and remote radio heads (RRH), as well as RF amplifierswhere gain may be similarly measured.

While various approaches to measuring the repeater or other wirelesscommunication system element gains are available, each approach has itsrelative advantages and disadvantages. One approach employed byembodiments of the invention measures and/or monitors front end (lownoise amplifier and down-converter) and back end (up-converter and poweramplifier) gains together. Some embodiments measure/monitor the frontand back end gains separately. Regardless of the approach, the gains maybe compared to predetermined threshold values for a determination of thestate of the device. Additionally, the approach may measure/monitor allof the front end and/or back end gains, or may only measure portions ofthose sections.

Overview

Embodiments of the invention employ methods to measure gain in a systemelement in a wireless communication system. These elements may includerepeater systems, distributed antenna systems (DAS), remote radio heads(RRH), and/or RF amplifiers as well as any combination of the elements.The determination of the gain in the embodiments is performed by themeasurement of the gain in various sections of the system element, whichare typically front-ends and back-ends. The system gain is thendetermined by multiplication (or addition if the gain measurements arein decibel) of the elements of a cascade. Methods for determiningfront-end and back-end gain are briefly presented with detaileddescriptions of the methods to follow.

In one embodiment for determining front end gain, a noise level in anunoccupied part of the receiver spectrum is measured. The front-endsection gain may be determined through the ratio of the measured noiselevel to an equivalent input noise level. The equivalent input noiselevel may be determined by the front-end section noise as a storedreference value for the various settings of the front-end section and athermal noise level at the current temperature, where the temperaturemay be determined by an on-board sensor. In an alternate embodiment fordetermining front end gain, the down-converter local oscillator may beshifted into a first receive band filter rejection band such that thereis an unoccupied part of the spectrum when a noise measurement may bemeasured. Once measured, the gain for this embodiment may be determinedsimilar to that of the embodiment above. Alternately, the receiveantenna may be disconnected by using a RF switch or otherwise suppressedto create an unoccupied part of the spectrum for a noise measurement.Gain may then be determined as set forth above.

In one embodiment for determining a back-end gain, a signal level may bemeasured at the input of the back-end. The signal at the output of theback-end may also be measured and the gain may then be determined fromthe ratio of the two measurements or the difference if the signals arerepresented as decibels. In an alternate embodiment, the signal levelmay be measured at the input to the back-end as well as a measurement ofthe spill-over of the back-end output that is received via apre-determined leakage of the duplexer filter or an over-the-air leakageof known value into the front-end of the opposite direction link. Theback-end gain may then be determined by determining the ratio betweenfront-end output of the signal level and back-end input underconsideration of the front-end gain as determined in an open band of thefront end as set forth above and the pre-determined leakage betweenfront-end and back-end. In another embodiment for determining back endgain, the signal level may be measured at the input to the back-end aswell as a measurement of the leakage of the back-end output that isreceived via an external, controllable, and determined leakage path ofknown value into the front-end of the same direction link. The back-endgain may then be determined by determining the ratio between front-endoutput of the signal level and back-end input under consideration of thefront-end gain as determined in using an open band of the front end asset forth above and the determined leakage between front-end andback-end.

The system element gain may be determined by the application of anycombination of the front end gain embodiments and the back end gainembodiments, which may be appropriate and suitable for the specificsystem. Additionally, the system gain, front-end section gain, orback-end section gain may be compared to a stored reference value. Anydeviation from this comparison exceeding a predetermined threshold maytrigger an alarm.

In general, back-end gain determination is more straight forward thanfront-end gain determination. Therefore, the discussion below will beginwith several methods for determining Back-End gain and then severalmethods for determining Front-End gain.

Back-End Gain

As used in this document, the “back-end” portion of the communicationsystem may be defined as all of the components from a reference point toan output antenna. This may include all, part, or none of a digitalsignal processing section close to an input of the back-end. Theback-end section of the system may include, in any order, one or moreamplifiers, one or more amplifiers plus one or more filters, one or moreamplifiers and filters plus one or more frequency mixers, or one or moreD/A converters with or without additional components. The back-endsection of the system may also include various other components such asattenuators and the like. Referring to the block diagram of an exemplaryrepeater 100 in FIG. IA, the “back-end” may include all of the mainsignal path elements from the signal power measurement receiverconnected to reference point 124 a or 124 b through the Duplexer 134.For the purpose of a back-end gain measurement a reference point 124 bmay be preferred as it would only measure the relevant signal spectrumthat will be fed into the back-end line-up. For the purpose of front-endmeasurements, reference point 124 a may be preferred, though eitherreference point may be used for either front-end or back-endmeasurements.

In some embodiments, power detector 120 may be a wide band elementconfigured to measure RMS power, but may as well be band-limited or timewindow limited. In other embodiments, a spectrum analyzer or a signalmeasurement receiver with configurable RF and IF measurement bandwidthsand configurable power detectors may be used as well. Still otherembodiments may employ an equivalent digital signal implementation of aband-limited or a band-unlimited power detector. The power detector maybe connected anywhere along the component line-up depending on thespecific needs.

Referring again to the block diagram of an exemplary repeater 100 inFIGS. 1A and 1B, when considering back-end gain determination, theamount of total composite power that digital sections 102, 104 (beforeupconverters 129, 133) are sending to the digital-to-analog converters(“DAC”) 106, 108 will already be known as it is easily computed from thedigitized signal waveform captured at reference point 124 a or 124 b inthe digital section 104. Composite power at the output of poweramplifiers (“PA”) 110, 112 is also readily measureable. With these knowncomposite power values, back end gain may be calculated by subtractionfor level values represented in decibels or signal level division iflinear level representations are used. These calculations use theassumption that no extra signals of significant power level aregenerated between the reference point 122 a or 122 b and the output ofpower amplifier 110 or the reference point 124 a or 124 b and the outputof power amplifier 112. Readings from power detectors 116, 120, 122, and124 and the corresponding exact transmit gain may be calibrated atfactory test time. Depending on the application, inexpensive powerdetectors, such as the LMV225/226/228 series from National Semiconductoror the MAX 2206/2207/2208 from Maxim, for example, may be used forback-end gain determination. These particular detectors offer a limiteddynamic range of approximately 30-40 dB.

For the downlink direction, 30-40 dB of range would likely besufficient. However, in the uplink direction, there may be times whenthe output level is too small to read with the power detectors 120, 124,which would potentially cause false failure alarms. These false alarmscould be avoided by using a higher dynamic range detector.Alternatively, an inexpensive detector may still be used if the gainmeasurement is disregarded any time the DAC 106, 108 drive level issmall. False alarms may then be avoided simply by ignoring thosereadings. In other words, the uplink transmitter gain would only bemonitored or measured when a “large enough” signal is present, forexample, greater than approximately −90 to −80 dBm at the repeaterinput, depending on repeater gain settings and maximum output power.

Front-End Gain

As used in this document, the “front-end” portion of the communicationsystem can be defined as everything between the input antenna and areference point of the system. This may include all, part, or none of adigital signal processing section close to the output of the front-end.The front-end section of the system may include, in any order, one ormore amplifiers, one or more amplifiers plus one or more filters, or oneor more amplifiers and filters plus one or more frequency mixers. Thefront-end section of the system may also include various othercomponents such as A/D converters 127, attenuators, and the like.Referring to the block diagram of an exemplary repeater 100 in FIG. IA,the “front-end” would comprise all of the main signal path elements,such as amplifiers and a down converter 125 having mixers, amplifiers,and filters to perform down conversion plus A/D converter 127, from theduplexer 134 through the signal power measurement receiver, powerdetector 122, capturing the signal at reference point 122 a or 122 b (Asimilar front end for the uplink direction would include all of the mainsignal path elements, such as amplifiers and a down converter 131 havingmixers, amplifiers, and filters for down conversion and A/D converter135). For the purpose of the front-end gain measurement a referencepoint 122 a before the filter may be preferred as it allows moreflexibility with respect to the frequency of the signal measurementtaken, though the reference point after the filter 122 b may also beused.

Power detectors 122, 124 may be implemented in a variety of ways. Thepower detector may be a wide band element configured to measure RMSpower, but for the purpose of the front-end gain, should beband-limited. The power detector may be time window limited as well. Aspectrum analyzer or a signal measurement receiver with configurable RFand IF measurement bandwidths and configurable power detectors may alsobe used. The equivalent digital signal implementation of a band-limitedor a band-unlimited power detector may be another alternative.

Detecting front-end gain presents a more challenging problem thanmeasuring back-end gain due to the unknown signals being received in theuplink and downlink directions. However, the overall repeater system hasan existing operational noise level that is known. The front-enddetection may utilize this known noise level and measure a differencebetween a threshold noise level that may be previously determined andstored (for example, during factory calibration) and an existingoperational noise level. The operational noise level is measured duringoperation of the repeater. The operational measurement may then becompared to the stored, calibrated noise floor. An operationalmeasurement resulting in a difference or delta that exceeds apre-determined threshold may indicate that a device or amplifier withinthe repeater has failed or is malfunctioning. While seemingly straightforward, the measurement of the operational noise in bands with signalscan be challenging.

A first embodiment of the front-end gain detection, as illustrated inthe graph 200 in FIG. 2, utilizes a band-limited noise power measurementin an unused segment 202 a, 202 b, 202 c of the band 204. The digitalsections 102, 104 may include built-in measurement receivers/powerdetectors 122, 124 as shown in FIGS. 1A and 1B. The power detectors 122,124 may be utilized to measure the noise floor 206 and compare it with astored/calibrated level that was previously measured. Any deviation fromthe original calibrated down converter gain, such as that caused byamplifier failure, temperature, or aging, may generally show up as adifference in noise levels. For example, if a device fails, theoperational noise floor will likely drop. The unused segments 202 a, 202b, 202 c may move within the band depending on where signals 208 arereceived, or the unused segments 202 a, 202 b, 202 c may be reservedsegments, or guard bands, used to isolate adjacent bands. While thisembodiment is simple to implement, it requires that there be at leastone unused band that can be utilized for the noise measurements.

When the band is fully occupied, the first embodiment above cannot beused. However, in some embodiments of the repeater 100 and asillustrated in the graph 300 in FIG. 3, the IF filters 126, 132 in FIGS.1A and 1B, together with any other intervening RF or IF filters that mayoptionally be included, may have a wider bandwidth 302 than thebandwidth 304 of the duplexers 134, 136. In some embodiments, the IFfilters may be implemented as SAW filters. Alternatively, the widerbandwidth filtering may be accomplished at baseband frequencies,implemented as analog and/or digital filters. Therefore, a usableportion 306 a, 306 b of the spectrum exists that sees the fulldown-converter gain but does not contain outside interference fromsignals 308 which would overwhelm the noise floor 310. Operational noisemay be measured in the bands 306 a, 306 b outside of the duplexer band304 and compared with the stored/calibrated level that was measuredduring factory test. As with the previous embodiment, any deviation fromthe original calibrated down converter gain, such as that caused byamplifier failure, temperature, or aging, may generally show up as adifference in noise levels.

For bands where the IF filters 126, 132 do not have extra bandwidth, thesystem may behave like the first front-end embodiment described above.Most applications may still have enough gaps between the receivedsignals due to frequency re-use patterns, guard bands, etc. that themeasurement receiver may find a reasonable noise floor. In the few caseswhich do not have gaps that allow precise measurement, failures may notbe able to be detected, however, there will also not be false “receiverfailure” alarms, because the signal level will be higher, not lower,than the calibrated noise level.

Situations and configurations may exist where the IF filters 126, 132 donot have extra bandwidth beyond the bandwidth of the duplexers, forexample, and as illustrated in the graph 400 in FIG. 4, the bandwidth402 of the IF filters 126, 132 is the same or narrower than thebandwidth 404 of the duplexers 134, 136. In an alternate embodiment forthis inventive configuration, the receiver may be intentionally mistunedto be briefly shifted as shown in the window 406 to look at a frequencyrange outside of the input duplexer filter bandwidth 404. Aftershifting, a usable portion 408 of the spectrum now exists that sees thefull down-converter gain but does not contain outside interference fromsignals 410, which would overwhelm the noise floor 412. In thisembodiment, local oscillators may be shifted by a few MHz and allow fora noise 412 measurement to be made in the small band 408 outside theduplexer bandwidth 404. As with the previous embodiment, any deviationfrom the original calibrated down converter gain, such as that caused byamplifier failure, temperature, or aging, may generally show up as adifference in noise levels. If thresholds are exceeded, failure alarmsmay be sent.

In some repeaters, the transmitters and receivers of the repeater mayhave separate local oscillators. This separation may allow for continuedrepeating of the vast majority of the band 414 during the shifting 406operation. In other embodiments, if the full bandwidth is not beingused, for example, the power detectors 122, 124 (FIGS. 1A and 1B) maylook to the unused portion first even though rest of band may be full.If there are no unused portions, briefly frequency shifting the duplexerband 404 may be performed as set forth above. In other embodiments, thefrequency shift may be permanently set during installation if there isno intention to repeat signals near one of the band edges.

Frequency shifting may also be implemented in an embodiment having a IFfilter with a bandwidth greater than the duplex filter. If thebandwidths are close, the input signal band may be shifted toward oneend of the IF filter band, creating a larger band for noise measurement.In this embodiment, the full signal (duplexer) bandwidth may beprocessed by adjusting the up-converter to shift the band back. Othercombinations of the above embodiments may also be made to facilitatenoise measurements for evaluating the front-end gains.

In an alternate embodiment of the repeater 500 in FIGS. 5A and 5B, highisolation switches 550, 552 may be implemented after the duplexerfilters 534, 536, but before the low noise amplifiers 554, 556 at thefront-end. The switches 550, 552 terminate the antennas 558, 560 suchthat the receiver would be switched to purely noise input for a briefperiod of time. During the brief period with no signal from theantennas, noise may be measured anywhere in the communication band. Aswith the previous embodiments, power detectors 522, 524 may be utilizedto measure the operation noise and compare it with a stored/calibratedlevel that was previously measured. Again, any deviation from theoriginal calibrated down-converter gain, such as that caused byamplifier failure, temperature, or aging, may generally show up as adifference in noise levels, indicating a potential problem with therepeater 500. Because this embodiment completely interrupts therepeating function of the repeater, the switching and noise testingwould likely be performed during non-peak hours, with the interruptionsbeing of short durations, allowing for the noise testing to beaccomplished. The antennas 558, 560 would then be switched back andnormal operation of the repeater would then resume. In otherembodiments, the switches 550, 552 which terminate the antennas may bereplaced by other components that suppress signals received by theantennas without having to terminate the antennas 558, 560. Still otherembodiments may inject amplified signals which may be used for gaindetermination without having to terminate the antennas 558, 560.

Alternatively, a signal may be generated by a signal generator 574 thatcould be injected into the front end at 570 and 572. This may occur withthe antenna input suppressed or attenuated or by injecting amplifiedsignals as set forth above, depending upon the level of the signal. Thesignal type could include amplified noise, a continuous wave tone, orsome other signal type including a signal source modulated with a pseudorandom bit sequence. Utilizing this approach may assist in reducing thesuppression/attenuation requirement of the antenna input.

Gain Determination from Leakage Paths

In the embodiments discussed above, additional circuitry may be requiredfor the gain measurement of the back-end path or transmit path.Additionally, front-end and back-end gains are determined separately.Turning to the embodiment of the repeater 600 in FIG. 6, known leakagepaths in this embodiment allow for the measurement of the gain of boththe back-end transmit section and the front-end receive section (in itssimplest form represented by amplifiers 608 and 610, respectively) atthe same time as a combined measurement of front-end section andback-end section without the need, in some embodiments, for anyadditional hardware. Signal generation and measurements may beaccomplished in the digital signal processing sections of the repeaterwithout requiring hardware changes. The generation and measurements maybe accomplished, in some embodiments, with only updates to software, forexample.

One possible leakage path that may be used to determine the gain in bothfront-end and back-end sections in the repeater 600 may be leakage 602through the duplex filters 604 a and 604 b in duplexer 604. The duplexfilters 604 a, 604 b have predefined rejection of the transmit signalsin the receive band. The rejection may be determined and calibrated inthe factory over the entire frequency band. The signal received atsignal receiver 606 is a known signal strength representing the totalgain of the transmit and receive sections from the known gain ofamplifier 608, coupling of duplexer 604, and gain of amplifier 610. Thissignal may be system noise in an empty band as with the embodimentsdiscussed above, or alternatively in some embodiments, a pilot signalmay be generated from a pilot signal generator 612. The pilot signal maybe generated in an empty band and may be used to test the gain of thesystem. When the overall gain from either noise or the pilot signaldrops below a predetermined threshold, it is an indication that there isa problem likely with one of the amplifiers, either 608 or 610, or aproblem with the duplexer 604. Regardless of where the problem lies, therepeater would not be performing at an optimum level and would need tobe serviced. One advantage of this method is that the duplexer isincluded in the gain measurement, and therefore, any duplexer or filterfailure would be detected as well.

In some embodiments, the duplexer 604 may be replaced by two antennas.In this configuration, the back-end, amplifier 608, is connected toeither a filter 604 a followed by an antenna 620 or to an antenna 620directly. A second antenna 630 may either be connected directly or via afilter 604 b to the front-end, amplifier 610. The antennas may be placedclosely to each other with a known amount of isolation or leakagebetween them. Any of the back-end gain determination methods above maythen be applied.

In another embodiment, as seen in FIG. 7, the gain of the repeater 700could be measured by using a switchable artificial leakage path 702between the output 704 and the input 706 of the repeater 700. Theleakage path 702 allows the repeater 700 to switch in a known amount ofattenuation 708, 710 between the two ports of the RF repeater 700. Whenthe switch 712 is closed, completing leakage path 702 the gain throughthe leakage path 702 contains the chain of gain of amplifier/back-end714, loss of duplexer 716, attenuations 708 and 710, loss of duplexer718, and gain of amplifier/front-end 720 and filter 740. This leakagegain may be received at signal receiver 722 and compared against athreshold as with the embodiments above. The leakage gain represents thesystem gain since the gains of the amplifier paths 714 and 720 areknown. The losses of the duplexers 716 and 718 are calibrated at thefactory and the attenuations 708 and 710 may be set to known values.Therefore the signal receiver 722 may monitor the gain through theleakage path 702 when switch 712 is closed and determine if there areproblems with any of the amplifiers or duplexers that would requireservice to the repeater. As with the embodiments described above, noisemeasurements may be used to check for failures, or the system may use asignal generated by pilot signal generator 724 as set forth in moredetail below. This configuration also assumes that all natural leakagepaths, such as paths 730 and 732 are significantly lower than theleakage path 702.

In an alternate embodiment of a repeater 800 illustrated in FIG. 8, thetransmit section gain from amplifier/back-end 802 may be monitored bythe receive path signal receiver 804. The leakage 806 in the duplexer808 between section 808 a and 808 b should be well calibrated to ensureaccurate monitoring. The signal receiver 804 and amplifier/front-end 810should also have bandwidths that are wide enough in their frequencyrange to partially or fully cover the frequency range of the transmitsection through amplifier 802 as well. The amplifier/front-end 810 mayalso be tuned to the transmit frequencies for a short time to performthe gain measurement.

In some embodiments, the duplexer 808 may be replaced by two antennas.In this configuration, the back-end 802 may be connected to either afilter 808 a followed by an antenna 820 or to an antenna 820 directly. Asecond antenna 830 may either be connected directly or via a filter 808b to front-end 810. The antennas are placed closely to each other with aknown amount of isolation or leakage between them. Any of the back-endgain determination methods above may then be applied.

Alternatively, a pilot signal may be generated in the transmit sectionusing pilot signal generator 812. In some embodiments, the pilot signalgenerator 812 may generate a signal 814 on a frequency that is close tothe receive band. The pilot signal frequency may also be outside of thetransmit band. This may assist in suppressing the pilot signal at theantenna terminals, as it assists in preventing the pilot signal frombeing transmitted as high level interference in the wirelesscommunication system. At the same time, the frequency may allow thereceive amplifier/front-end 810 to receive the pilot signal withouthaving to de-tune its synthesizer. The pilot signal does need toovercome a duplexer rejection (which is lowest at the cross-over pointwhere the attenuation over frequency characteristics of filter 808 b andfilter 808 a intersect) and the equivalent noise level of the receiveamplifier/front-end 810.

Implementing digital signaling processing with digitized intermediatefrequency signals in some embodiments would potentially allow the simpleaddition of this feature without any changes to the printed circuitboards. The pilot signal 814 may be generated in the digital section oran amplified signal of a repeated wireless standard could be usedinstead. The measurement receiver may also be implemented in the digitalsection as well. Adding the gain measurement capability to an existingdigital RF repeater may only require a software update. The duplexerrejection could be either calibrated or, for an already deployed system,measured in a learning phase. After calibration or termination oflearning phase, a variation from the expected number would represent again change in either amplifier/back-end 802 or amplifier/front-end 810.The gain of amplifier/front-end 810 may be determined from a noisemeasurement. The combination of both would then allow the measurement ofthe gain of amplifier/back-end 802.

Alarm Determination

By determining front-end and back-end gains independently of oneanother, at least four possible alarm conditions may exist. Theseinclude downlink front-end, downlink back-end, uplink front-end, anduplink back-end. Any failures determined from the gain measurements ofthe front-end and back-end of the uplink and downlink directions maythen be sent upstream, either as a separate uplink message, or alongother control or network lines that may be connected to the repeater.The location of the alarm may also prove useful for repair orreplacement, if only portions of the repeater electronics need to bereplaced or repaired.

As set forth above with respect to front-end gain determination, this isprimarily accomplished in the existing power detectors 122, 124 in thedigital processing components 102, 104 as seen in FIGS. 1A and 1B. Asseen in flowchart 900 in FIG. 9A, the operational noise spectrum isobtained from the spectrum analyzer by one of the methods set forthabove for the downlink direction (block 902). The noise level that waspreviously calibrated and stored is then retrieved (block 904). Acomparison of the measured operational noise in the downlink directionis made with previously stored/calibrated noise values (block 906). Ifthe downlink noise is not within a specified tolerance (“No” branch ofdecision block 908), then an alarm for the downlink front end isgenerated (block 910) and transmitted either through an uplink messageor other communication with the repeater. If the noise is withintolerance (“Yes” branch of decision block 908), tests can begin again atblock 902.

Similar operations occur for front-end gain determination for the uplinkdirection. As seen in flowchart 950 in FIG. 9B, the operational noisespectrum is obtained from the spectrum analyzer by one of the methodsset forth above for the uplink direction (block 952). The noise levelthat was previously calibrated and stored is then retrieved (block 954).A comparison of the measured operational noise in the uplink directionis made with previously stored/calibrated noise values (block 956). Ifthe uplink noise is not within a specified tolerance (“No” branch ofdecision block 958), then an alarm for the uplink front end is generated(block 960) and transmitted either through an uplink message or othercommunication with the repeater. If the noise is within tolerance (“Yes”branch of decision block 958), tests can begin again at block 952. Testsfor either the uplink or downlink directions may be continuous orperformed at specific intervals. For the embodiments where the antennais switched off, tests may occur less frequently, for example once ortwice during off-peak times.

As set forth above, back-end gain may be determined from the differenceof the power measured at the output of the power amplifier and the knownsignal level at the input of the digital-to-analog converter (DAC). Theprocess for the downlink direction may be seen in flowchart 1000 in FIG.10A. Power levels at the input of the downlink DAC are computed (block1002) from the digitized signal waveform in the digital section of therepeater. If the input to the DAC is below a specified threshold value(“No” branch of decision block 1004), then the gain determination andfault assessment are skipped, and the process may begin again at block1002. If, however, the input to the DAC is above a specified threshold(“Yes” branch of decision block 1004), then the power level is obtainedfrom the downlink power amplifier (block 1006). The power ratio (ordifference, if the power levels are measured in dB) is then calculatedto determine the back-end gain (block 1008). The power ratio ordifference may be determined using hardware, or hardware and software.For example, as seen in FIGS. 1A and 1B, one or more FPGAs 170, 172 maybe utilized to determine the difference and perform the comparison.Similarly other special ASICs or other programmable chips may be used.Furthermore, the repeater 100 may be controlled by a controller (notshown) and the controller may determine the differences and otherthreshold comparisons. If the backend gain does not meet a specifiedtolerance (“No” branch of decision block 1010), then an alarm for thedownlink back-end is generated (block 1012) and transmitted eitherthrough an uplink message or other communications with the repeater. Ifthe back-end gain is within tolerance (“Yes” branch of decision block1010), tests may begin again at block 1002.

Similarly for the uplink side, the process may be seen in flowchart 1050in FIG. 10B. Power levels at the input of the uplink DAC are computed(block 1052) from the digitized signal waveform in the digital sectionof the repeater. If the input to the DAC is below a specified thresholdvalue (“No” branch of decision block 1054), then the gain determinationand fault assessment are skipped, and the process may begin again atblock 1052. If, however, the input to the DAC is above a specifiedthreshold (“Yes” branch of decision block 1054), then a power level isobtained from the uplink power amplifier (block 1056). The power ratio(or difference, if the power levels are measured in dB) is thencalculated to determine the back-end gain (block 1058). Similar to thedownlink side, the power ratio or difference may be calculated usinghardware, or hardware and software. If the backend gain does not meet aspecified tolerance (“No” branch of decision block 1060), then an alarmfor the uplink back-end is generated (block 1062) and transmitted eitherthrough an uplink message or other communications with the repeater. Ifthe back-end gain is within tolerance (“Yes” branch of decision block1060), tests may begin again at block 1052. Because there is nointerruption to the signals when calculating and comparing back-endgains, these tests may be performed at any time. In some embodiments,determination of the front-end and back-end gains may be coordinated. Inother embodiments, they may be checked independently of one another.

While the present invention has been illustrated by a description of oneor more embodiments thereof and while these embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail. Themethodology that the embodiments of the invention cover applies not onlyto RF repeaters, but is also applicable to at least Distributed AntennalSystems (“DAS”) and remote radio heads. The methodology of theembodiments of the invention disclosed herein is generic enough tomeasure gain in all the additional above mentioned types of equipment aswell as other related devices where gain may be measured. Additionaladvantages and modifications will readily appear to those skilled in theart. The invention in its broader aspects is therefore not limited tothe specific details, representative apparatus and method, andillustrative examples shown and described. Accordingly, departures maybe made from such details without departing from the scope of thegeneral inventive concept.

What is claimed is:
 1. A signal repeating device for repeating signalsin a wireless communication system, the signal repeating devicecomprising: signal path elements for defining at least an uplink signalpath or a downlink signal path in the signal repeating device, thesignal path elements including: frequency conversion circuitry; filtercircuitry; amplifier circuitry; circuitry configured for obtaining anoperational noise measurement in a signal path of the signal repeatingdevice and for measuring an operational noise level in a frequency bandthat is outside of and adjacent to a bandwidth of a first elementlocated in the signal path; circuitry configured for retrieving a storedparameter that includes a previously determined reference noise levelfor the signal repeating device and comparing the measured operationalnoise level to the retrieved reference noise level parameter and usingthe comparison to evaluate the gain of at least a section of the signalrepeating device to determine a failure or malfunction of an element inthe signal repeating device.
 2. The signal repeating device of claim 1,wherein the frequency band for measuring the operational noise level iswithin a wider bandwidth of a second, subsequent element in the samesignal path as the first element.
 3. The signal repeating device ofclaim 1 further comprising: circuitry configured for tuning an inputfrequency band of the signal repeating device to shift the inputfrequency band of the signal path partially or completely outside of abandwidth of the first element to create an open frequency band that isoutside of and adjacent to the bandwidth of the first element formeasuring an operational noise level in the created open frequency band.4. The signal repeating device of claim 1, further comprising circuitryfor generating an alarm when the operational noise level is outside of aspecified tolerance with respect to the stored parameter.
 5. The signalrepeating device of claim 1, further comprising: digital-to-analogcircuitry in the signal path configured for forming a digital section inthe signal path; digital processing circuitry configured for computing apower level at a point in the digital section of the signal path;circuitry for measuring a power level at a point in a back end of thesignal path and calculating a gain for a section of the signal repeatingdevice using the measured back end power level and the computed powerlevel in the digital section.
 6. The signal repeating device of claim 5,further including circuitry configured for comparing the calculated gainto a predetermined range.
 7. The signal repeating device of claim 6,wherein the circuitry is configured, in response to the calculated gaindeviating from the predetermined range, for generating an alarmindicative of the gain deviation.
 8. The signal repeating device ofclaim 1, wherein the stored parameter includes a gain and a referencesignal.
 9. The signal repeating device of claim 1, wherein the signalrepeating device is selected from a group consisting of: a repeater, adistributed antenna system, and a remote radio head.
 10. The signalrepeating device of claim 1, wherein the first element is selected froma group consisting of: an RF filter, an IF filter, and a digital filter.11. A signal repeating device for repeating signals in a wirelesscommunication system, the signal repeating device comprising: signalpath elements for defining at least an uplink signal path or a downlinksignal path in the signal repeating device to couple to an antenna, thesignal path elements including: frequency conversion circuitry; filtercircuitry; amplifier circuitry; circuitry configured for obtaining anoperational noise measurement by suppressing an input signal from anantenna coupled to a signal path by disconnecting the antenna in thesignal path and for measuring an operational noise level in a frequencyband that is within a bandwidth of the signal repeating device;circuitry configured for retrieving a stored parameter that includes apreviously determined reference noise level for the signal repeatingdevice and comparing the measured operational noise level to theretrieved reference noise level parameter and using the comparison toevaluate the gain of at least a section of the signal repeating deviceto determine a failure or malfunction of an element in the signalrepeating device.
 12. The signal repeating device of claim 11 furthercomprising circuitry for generating an alarm when the operational noiselevel is outside of a specified tolerance with respect to the storedparameter.
 13. The signal repeating device of claim 11 wherein theamplifier circuitry is configured for amplifying the operational noiselevel prior to the noise level measurement.
 14. The signal repeatingdevice of claim 11, further comprising a signal generator configured forintroducing a pilot signal prior to the operational noise levelmeasurement.
 15. A signal repeating device for repeating signals in awireless communication system, the signal repeating device comprising:signal path elements for defining at least an uplink signal path or adownlink signal path in the signal repeating device to couple to anantenna, the signal path elements including: frequency conversioncircuitry; filter circuitry; amplifier circuitry; circuitry configuredfor capturing a leakage signal from a defined leakage path in the signalrepeating device using a signal receiver and for evaluating the gain ofthe leakage signal, the defined leakage path reflecting the gain of asignal passing through elements of the signal repeating device; andcircuitry configured for comparing the gain of the leakage signal to apredetermined threshold that is a function of gain and attenuationcharacteristics of elements of the signal repeating device that arelocated in the defined leakage path and for using the comparison todetermine a failure or malfunction of an element in the signal repeatingdevice.
 16. The signal repeating device of claim 15, further comprising:circuitry configured for measuring a signal level in the leakage path atan input to a back-end of the signal repeating device; circuitryconfigured for measuring a portion of an output signal of the back-endthat is received via a pre-determined leakage path to a first element oran over-the-air leakage path of a known value into a front-end of anopposite direction signal path of the signal repeating device; circuitryconfigured for determining a back-end gain by determining a ratiobetween a front-end output of the signal level and back-end input usinga front-end gain and the pre-determined leakage between front-end andback-end wherein the front-end gain is determined by measuring anoperational noise level in an open band.
 17. The signal repeating deviceof claim 15 further comprising a switch in the leakage path that isselectively closed to capture the leakage signal.
 18. The method ofclaim 17, wherein signals from natural leakage paths are significantlylower than the leakage signal from the switched leakage path.
 19. Thesignal repeating device of claim 15 further comprising a signalgenerator for introducing a pilot signal into the leakage path such thatthe captured leakage signal contains at least a portion of the pilotsignal.
 20. The signal repeating device of claim 15, wherein the signalrepeating device is in a form selected from a group consisting of: arepeater, a distributed antenna system, and a remote radio head.